1. Field of the Invention
The present invention relates to an image processing apparatus, an imaging apparatus, an image processing method, and a computer program product.
2. Description of the Related Art
In recent years, in the field of digital still cameras (hereinafter, “digital cameras”), an increase in the number of pixels of a charge-coupled device (CCD) or an imaging device has been achieved. On the other hand, such an increase in the number of pixels of the CCD poses a problem of a decrease in sensitivity of the CCD.
To solve such a problem, an imaging apparatus in which pixels of a plurality of images are added is disclosed (see Japanese Patent Application Laid-Open No. 2005-44915). In such an imaging apparatus, pixels of images are added to increase sensitivity.
Also, another imaging apparatus is disclosed (see Japanese Patent Application Laid-Open No. 2005-303519) in which a pixel signal for adding pixel values of adjacent pixels together is output to increase sensitivity.
Furthermore, a technology is also disclosed (see Japanese Patent Application Laid-Open No. 2004-297731) in which, although noise is enhanced when an image is shot with increased sensitivity, a cut-off frequency of a low-pass filter is set according to imaging sensitivity to remove noise.
However, in the technology disclosed in Japanese Patent Application Laid-Open No. 2005-44915, with the addition of the pixels of the images, an exposure time is increased. There is no problem if the camera is fixed and the subject does not move. However, if either one of the camera or the subject moves a positional deviation will disadvantageously occur.
Also, in the technology disclosed in Japanese Patent Application Laid-Open No. 2005-303519, pixel values of adjacent pixels are added together, thereby causing a problem of decreasing resolution.
Moreover, in the technology disclosed in Japanese Patent Application Laid-Open No. 2004-297731, although noise can be removed according to imaging sensitivity, the edge of the image is blurred. For example, if sensitivity is set high when imaging is performed at a lighted place, a blurring process may have a strong effect on an image even with less noise, thereby causing the image to be blurred more than necessary.
Still further, in the technology disclosed in Japanese Patent Application Laid-Open No. 2004-297731, when the exposure time is short at the time of imaging, color reproducibility and white balance are deteriorated, and the balance between color and luminance of the image is not improved even noise is removed.